the chemistry of chocolate - american chemical society...chocolate liquor and 12% whole milk...

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The Chemistry of Chocolate and Desire

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Brian Guthrie Corporate Research Fellow,

Cargill

Michael TunickAssistant Clinical Professor, Culinary Arts

& Food Science, Drexel University

Michael H. Tunick

Center for Food & Hospitality Management

Drexel University, Philadelphia, PA


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A semi-solid suspension of fine solid particles from sugar and cocoa (〜70% total) in a continuous fat phase

Cocoa solids are derived from beans obtained from the fruit of Theobroma cacao

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What Is Chocolate?

Zarrillo et al., Nature Ecology & Evolution, Oct. 29, 2018

Cacao previously thought to have been first domesticated in Mesoamerica

Greatest diversity found to be in upper Amazon region

Archaeological evidence: cacao starch grains, absorbed theobromine residues, and DNArecovered from site in southeast Ecuador

• Dated to 〜 5,300 years ago

Earliest evidence of T. cacao use in the Americas and the first unequivocal archaeological example of its pre-Columbian use in South America

Upper Amazon region is oldest center of cacao domestication yet identified

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Origin

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Manufacture

http://chocolateproducing.blogspot.com/2009/05/process-of-chocolate-manufacturing.html

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Fermentation

• Takes place in baskets, wooden boxes, or heaps stored away from light, depending on local custom

• Beans turned to ensure even fermentation

• Process lasts 5-7 days, depending on cultivar and variety

http://chocolateproducing.blogspot.com/2009/05/process-of-chocolate-manufacturing.html

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Fermentation: First Day

Anaerobic, exothermic reactions, temperature to 40°C

Yeast ferments sucrose, glucose, fructose

Aeration from turning beans, temperature to 50°C

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Fermentation: Next Day

Germ within bean dies from heat, alcohol, and acetic acidEnzymes within bean released, important for flavor

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Yield: 80-85% well fermented beans

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Fermentation: Last Days

Browning reactions of polyphenol with proteins and peptides produce colors characteristic of cocoa

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Fermentation and Drying

Help remove natural tannins and acids present

• Tannins: 5-15% of bean by weight

• Bring astringent and bitter flavor to final chocolate

Drying limits mold growth, moisture content goes from 60 to 7.5%

• Sun-drying preferred

• Artificial drying may lead to off-flavors

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Why is it called Baker’s Chocolate?

Audience Survey QuestionANSWER THE QUESTION ON BLUE SCREEN IN ONE MOMENT

• It is used in baking

• It originated in the Baiker region of West Africa

• It was named after a guy named Baker

• Nobody knows

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Chocolate Types

Baker’s chocolate/bitter chocolate/unsweetened chocolate: made from pure chocolate liquor (100% cacao with no sugar added)

Bittersweet chocolate: sweetened dark chocolate with sugar and cocoa butter and ≥ 35% chocolate liquor (70-100% cacao)

Semisweet chocolate: dark, sweetened chocolate made with ≥ 15% chocolate liquor

1918 Ad Walter Baker Co Beverage La Belle Chocolatiere Boy Scout Kid Cocoa

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Chocolate Types

Milk chocolate: In US, must contain ≥ 10% chocolate liquor and 12% whole milk (usually in dried form)

• Bars of fine milk chocolate generally contain 30-45% cacao

• Cheapest can have as little as 5% cacao

Dark chocolate: 15-35% chocolate liquor with cocoa butter, vanilla, sugar, or other sweetener, and usually lecithin as an emulsifier

White chocolate: cocoa butter (≥ 20% in US), sugar, milk powder, spices such as vanilla

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Milk Chocolate

Milk solids added

Milk fat: 15-20% solid at ambient temperature

• Softens chocolate texture, used at ≤ 30% of total fat content

• Inhibits fat bloom

Milk proteins add to perceived creaminess

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Sensory Attributes

Appearance: smooth, shiny, mahogany-black

Sound: clear and crisp snap when broken

Touch: should quickly start to melt in hand with no graininess in mouth

Smell: fruits, nuts, spices, flowers, sugar, etc.

Taste: bitterness with hint of acidity, sweetness with suggestion of sourness, touch of saltiness, plus characteristic flavors

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Snap

Good, clean snap indicates high cacao content and well-tempered chocolate

Too dry if it splinters, too waxy if it resists breaking

Milk chocolate (lower levels of cocoa solids) and white chocolate (no cocoa solids) do not have the same snap

Opposite: crumbly

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Texture

Mouthfeel and textural properties determined by unique properties of cocoa butter

Careful processing and selection of ingredients necessary to produce desirable properties

Viscosity controlled by addition of cocoa butter and surface-active ingredients (lecithin)

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Particle Size

Optimization requires consideration of palate sensitivity

Product is perceived as gritty or coarse in the mouth if maximum particle size > 30 μm

Chocolate milled to maximum particle size of 20 μm will have creamier taste and texture than that with 30 μm

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Cocoa Butter

Most critical raw material for chocolate

Tree, flower, pod, seed, and postharvest handling all different from those of any other food ingredient

Triglycerides primarily palmitic acid (27%), stearic acid (34%), and oleic acid (34%)

• Structure leads to unique solidification and liquefying properties

• Manufacturer can work with chocolate in ways that no other foods permit

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Tempering

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The Six Polymorphs of Chocolate

https://www.compoundchem.com/2014/04/19/the-polymorphs-of-chocolate

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Flavor and Color

Determined by processing variables and inherent characteristics of the cocoa bean

Flavor precursors develop during fermentation and primarily interact at roasting temperatures

Complex browning reactions occur during roasting

Numerous heterocyclic flavor compounds

produced then contribute to the characteristic chocolate flavor

https://www.compoundchem.com/2014/04/19/the-polymorphs-of-chocolate

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Maillard Reaction

Non-enzymatic reaction between amino acid and reducing sugar

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Pyrazines

Primary odor components

〜 80 contribute to overall flavor

Most originate from α-aminoketones by Streckerdegradation and Maillard reactions during roasting

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Esters

Second most important odor components

Arise from amino acids and fermentation

Long chain esters produce undesirable fatty and waxy flavors

Ethyl-2-methylbutanoate

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Alcohols

Arise during fermentation from microbial activity

May also result from heat degradation of amino acids

2-phenylethanol: most odor-active compound in dried and fermented cocoas

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Aldehydes and Ketones

Formed during fermentation

Aldehydes also arise from Streckerdegradation of amino acids during roasting

• Needed for pyrazine formation

3-Methylbutanal

2-phenylacetaldehyde

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Acids

Acetic acid most odor-active

Short chain acids mostly removed during processing

Lead to undesirable odors

3-Methylbutyric acid

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Furanones and Pyrones

Produced by degradation of monosaccharides during drying and roasting

• Confer pleasant caramel notes and enhance flavor impression

• Destroyed during alkalization

Furaneol Maltol

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Pyrrole

2-Acetyl-1-pyrrole produced during drying and roasting via Maillard reactions and Strecker degradation, starting from proline

• Confers caramel, chocolate, and roasted desirable notes

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Other Compounds

Alkaloids, including theobromine (3,7-dimethylxanthine) and caffeine (1,3,7-trimethylxanthine)

• Bitter taste

Polyphenols in 3 main groups: catechins (flavan-3-ols), anthocyanins, and proanthocyanidins

• Astringent and bitter tastes

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Cravings

Most craved substance in US (Michener and Rozin, 1994; Osman et al., 2006)

Effects attributed to texture, sweetness, fat, aroma, and specific compounds

Xanthines implicated in cravings

Physiol Behav 1994, 56:419; Appetite 2006, 47:290

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What happens in Japan on Valentine’s Day?

Audience Survey QuestionANSWER THE QUESTION ON BLUE SCREEN IN ONE MOMENT

• Men give chocolate to women

• Women give chocolate to men

• Adults give chocolate to children

• Children give chocolate to their parents

• Nothing – The Japanese don’t celebrate the day

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Methylxanthines in Cocoa

Caffeine metabolite

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Theobromine

Nehlig Br J Clin Pharmacol 2013, 75:716; Psychopharmacology 2004, 176:412

From Greek θεός (god) + βρῶμα (food)

100 g milk chocolate contains 〜150 mg

100 g very dark chocolate contains ≤ 440 mg (Nehlig, 2013)

Significant effects (mood and behavior changes) not seen below 560 mg theobromine in most people (Smit et al., 2004)

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Caffeine

From French café (coffee)

100 g milk chocolate contains 〜20 mg

100 g dark chocolate contains 〜43 mg

White chocolate has none

Increases alertness, mental energy, and cognitive and psychomotor performance

• Also small increase in feelings of well-being

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Caffeine’s Mechanism of Action

Adenosine: central nervous system neuromodulator with specific receptors

Upon binding to receptors, neural activity slows, creating sleepiness

• Dilates blood vessels to ensure good oxygenation during sleep

Caffeine acts as adenosine-receptor antagonist

• Binds to same receptors but without reducing neural activity

• Fewer receptors available to natural braking action of adenosine, and neural activity increases

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Caffeine’s Mechanism of Action

Causes pituitary gland to secrete hormones that cause adrenal glands to produce more adrenalin

• Increases energy level and alertness

• Increases production of dopamine in brain’s pleasure circuits

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Phenylethylamine

Related to amphetamines, releases dopamine

Derived from phenylalanine in body or by microbes

Typically 50-100 mg in 100 g chocolate bar

Quickly metabolized by monoamine oxidase B

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Anandamide

From Sanskrit ananda (bliss) + amide

First described in 1992

50 μg/100 g cocoa bean (Nehlig, 2013)

Metabolite of arachidonic acid (20:4)

Fatty acid neurotransmitter

Endocannabanoid

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Anandamide Experiments

Neural receptors same ones to which THC binds

Hypothesis: endogenous cannabinoid system plays role in regulation of appetite and food intake, involved in reward processes that mediate incentive or hedonic value of food

Experiments conducted on rats injected with anandamide and fed sugar and quinine solutions

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Anandamide Results

Neuropsychopharmacology 2007, 32:2267

Anandamide specifically amplifies hedonic impact of sweetness (prototypical sensory pleasure)

Rewarding and euphoric effects of exogenous cannabinoid drugs (such as THC) mediated by same endocannabinoid hedonic hotspot that amplifies taste ‘liking’

Mahler et al., 2007

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Anandamide

Might contribute to feeling of well-being

• But rapidly broken down by fatty acid amide hydrolase

• > 30 kg chocolate to experience effects comparable to 1 dose of cannabis

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Magnesium

Med Hypoth 2006, 67:362; J Affect Disord 2006, 92:149

Deficiency implicated in major depression (Eby and Eby, 2006)

Craving proposed as response to Mg deficit

100 g milk chocolate contains 〜63 mg Mg

100 g dark chocolate contains 〜146 mg Mg

Foods high in Mg not craved, do not satisfy craving for chocolate (Parker et al., 2006)

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Possibilities

Simultaneous activation of dopamine and opioid systems seen with ingestion of high fat/sugar foods

Similar to effects by dopamine agonists (amphetamine, cocaine) and opioid agonists (heroin, morphine)

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Dopamines

Chocolate may interact with some neurotransmitter systems such as dopamine(chocolate contains dopamine precursor tyrosine), serotonin, and endorphins (contained in cocoa and chocolate)

• Contribute to appetite, reward and mood regulation

Contribution of dopaminergic system to chocolate craving and eating likely to be general, not chocolate specific

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Opioids

Intake of sweet food increased by opiate agonists and decreased by opiate antagonists

Opioid system plays role in palatability of preferred foods

• Endorphins released during eating could enhance pleasure of eating

• Chocolate stimulates endorphin release

Opioids can stimulate immediate release of beta-endorphin in hypothalamus

• Produces analgesic effect

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Serotonin

After ingestion of carbohydrates, brain serotonin concentrations rise only when protein component of meal < 2%

Chocolate contains 5% of calorie content as protein

• Negates any serotonin effect

Extreme dietary manipulations of tryptophan (serotonin precursor) result in physiological changes

• Too slow to account for mood effects described during or soon after eating chocolate

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Human Study

Physiol Behav 2011, 104:117

Tested on 280 passersby given 12.5 g chocolate

Nasser et al., 2011

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Human Study

Tasting had measurable psychoactive effects, associated with desire to consume more

Desire proportional to sugar and fat contents and percent of cocoa

Sample with sorbitol instead of sucrose produced same results as 0 and 38% sucrose samples (all had 56% sugar)

Binding to sweet receptor (rather than taste of sugar) plays role in triggering psychoactive effects

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Men vs. Women

Men had significantly lower chocolate craving and liking scores

When asked how much more chocolate they would like to consume, men asked for 4 pieces and women 3 pieces

Women concerned with weight?

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Explanation of Craving

Composite sensory properties more likely to play prominent role in chocolate liking or craving

If caloric deficit motivates chocolate craving, both milk chocolate and white chocolate should appeal equally, but don’t

If psychoactive substances or Mg deficit motivate chocolate craving, both milk chocolate and unsweetened cocoa powder should appeal equally, but don’t

Probably learned emotion

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Aphrodisiac

Codex Nuttall, Oaxaca, 1051 AD

Definition: substance that increases libido

Derived from Aphrodite, Greek goddess of love

Aztecs first to attribute cocoa bean and sexual desire

Idea brought to Europe by Spanish

Eight Deer Jaguar Claw receiving chocolate from bride, 13 Serpent

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Desirable Compounds

Amounts of phenylethylamine, anandamide, etc., in chocolate too small to have any measurable effect on desire

Compounds broken down too fast

Phenethylamine Anandamide

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Aphrodisiac Qualities

Studies find no direct link between chocolate consumption and heightened sexual arousal

Aphrodisiac qualities probably psychological and not physiological

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Books For Further Reading

Catherine Atkinson et al., The Chocolate and Coffee Bible, Hermes House, 2009. Mostly recipes, but also history and baking techniques.

Stephen T. Beckett, The Science of Chocolate, 2nd edition, RSC Publishing, 2008. Details processing procedures, analyses, and nutrition.

Harold McGee, On Food and Cooking, Scribner, 2004. The science and lore of chocolate and any other food you can think of.

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Cargill




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ACS Division of Agricultural & Food Chemistry

AGFD brings together persons particularly interested in the chemistry of agricultural and food products, both raw and finished; to foster programs of general papers and symposia on special topics dealing with this field of chemistry; to promote such other activities as will stimulate activity in and emphasize the importance of research in agricultural and food chemistry.




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Cargill



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Conclusions and Final Thoughts

Compounds in chocolate not present in high enough concentrations (theobromine), do not contribute to craving (caffeine, Mg), broken down too quickly (phenylethylamine, anandamide), or too slowly (carbohydrates/serotonin) to produce aphrodisiac effect

Chocolate cravings probably stem from flavor, texture, aroma, and psychology more than specific compounds

Be a featured fan on an upcoming webinar! Write to us @ [email protected] 74

“This was a great opportunity to learn about applications of chemistry to coffee and find inspiration for how to make chemistry relatable to non-chemists. Overall very engaging and a highly successful webinar!”

Carolyn VircaPostdoctoral Associate, Berlinguette Research,ACS member for 2 years strong!



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@AmerChemSociety

https://www.linkedin.com/company/american-chemical-society

@AmerChemSociety

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Chemical & Engineering News (C&EN) The preeminent weekly digital and print news source.

NEW! ACS SciFinder ACS Members receive 25 complimentary SciFinder® research activities per year.

NEW! ACS Career Navigator Your source for leadership development, professional education, career services, and much more.


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the chemistry of chocolate - american chemical society...chocolate liquor and 12% whole milk...

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